/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.googlecode.coss.common.utils.xml;

import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;

import com.googlecode.coss.common.utils.lang.exception.Assert;

/**
 * Contains common behavior relating to {@link javax.xml.transform.Transformer
 * Transformers}, and the <code>javax.xml.transform</code> package in general.
 * 
 * @author Rick Evans
 * @author Juergen Hoeller
 * @since 2.5.5
 */
public abstract class TransformerUtils {

    /**
     * The indent amount of characters if
     * {@link #enableIndenting(javax.xml.transform.Transformer) indenting is
     * enabled}.
     * <p>
     * Defaults to "2".
     */
    public static final int DEFAULT_INDENT_AMOUNT = 2;

    /**
     * Enable indenting for the supplied {@link javax.xml.transform.Transformer}
     * .
     * <p>
     * If the underlying XSLT engine is Xalan, then the special output key
     * <code>indent-amount</code> will be also be set to a value of
     * {@link #DEFAULT_INDENT_AMOUNT} characters.
     * 
     * @param transformer the target transformer
     * @see javax.xml.transform.Transformer#setOutputProperty(String, String)
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void enableIndenting(Transformer transformer) {
        enableIndenting(transformer, DEFAULT_INDENT_AMOUNT);
    }

    /**
     * Enable indenting for the supplied {@link javax.xml.transform.Transformer}
     * .
     * <p>
     * If the underlying XSLT engine is Xalan, then the special output key
     * <code>indent-amount</code> will be also be set to a value of
     * {@link #DEFAULT_INDENT_AMOUNT} characters.
     * 
     * @param transformer the target transformer
     * @param indentAmount the size of the indent (2 characters, 3 characters,
     *            etc.)
     * @see javax.xml.transform.Transformer#setOutputProperty(String, String)
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void enableIndenting(Transformer transformer, int indentAmount) {
        Assert.notNull(transformer, "Transformer must not be null");
        Assert.isTrue(indentAmount > -1, "The indent amount cannot be less than zero : got "
                + indentAmount);
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        try {
            // Xalan-specific, but this is the most common XSLT engine in any case
            transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount",
                    String.valueOf(indentAmount));
        } catch (IllegalArgumentException ignored) {
        }
    }

    /**
     * Disable indenting for the supplied
     * {@link javax.xml.transform.Transformer}.
     * 
     * @param transformer the target transformer
     * @see javax.xml.transform.OutputKeys#INDENT
     */
    public static void disableIndenting(Transformer transformer) {
        Assert.notNull(transformer, "Transformer must not be null");
        transformer.setOutputProperty(OutputKeys.INDENT, "no");
    }

}
